Aspirin dose increase from 75 to 150 mg suppresses red blood cell contribution to suboptimal platelet response to aspirin in patients with CAD.

PURPOSE: To verify the hypothesis that erythrocytes play a role in suboptimal blood platelet response to acetylsalicylic acid (ASA, aspirin) in subjects with coronary artery disease (CAD).

METHODS

In a cross-over randomized controlled intervention study we evaluated blood platelet response to 30-day treatment with 75 mg/d or 150 mg/d of ASA (enteric coated) in CAD patients (n = 125). In vitro platelet response to collagen or arachidonic acid was monitored with impedance aggregometry and plasma thromboxane B2 was assayed immunoenzymatically. Blood morphology and several plasma biochemical parameters were determined using routine diagnostic procedures.

RESULTS

CAD patients demonstrated lower blood platelet responsiveness to 75 mg/d of ASA compared to healthy subjects. The improved platelet responsiveness to 150 mg/d of ASA was particularly evident in "poor" responding patients. Positive correlations between platelet "poor" response to lower (75 mg/d) ASA dose and red blood cell count (Rs = 0.215; p < 0.04), haemoglobin (Rs = 0.232; p < 0.02) and haematocrit (Rs = 0.239; p < 0.02) were found in CAD patients. Association between "poor" platelet response with lower ASA dose was confirmed by conditional maximum likelihood logistic regression, which showed the independency between erythrocyte-derived parameters, as the risk factors for suboptimal platelet response to ASA, and other risk factors, like CRP or LDL-cholesterol. In "poor" ASA responders taking the higher ASA dose (150 mg/d) the correlation between platelets' response to ASA and erythrocyte-derived parameters was not significant.

CONCLUSIONS

Red blood cell parameters are associated with suboptimal blood platelet response to ASA in patients with CAD. Such a platelet refractoriness to ASA may be effectively overcome by increasing the ASA dose.